Organic EL devices which utilize organic substances are expected to be useful for application as an inexpensive full color display device of the solid light emission type having a great size and various developments on the organic EL devices are being conducted. In general, an organic EL device has a construction comprising a light emitting layer and a pair of electrodes sandwiching the light emitting layer. The light emission of the organic EL device is a phenomenon in which, when an electric field is applied between the two electrodes, electrons are injected from the cathode side and holes are injected from the anode side, the electrons are recombined with the holes in the light emitting layer to form an excited state, and energy generated when the excited state returns to the ground state is emitted as light.
As compared with an inorganic light emitting diode, conventional organic EL devices requires high driving voltage and only exhibited low luminance or low efficiency of light emission. Moreover, characteristic degradation of the conventional organic EL devices was also extravagant and as a result, they were not practically used. Although recent organic EL devices are improved step by steps, it has been still demanded to develop organic EL devices operable at low driving voltage, with excellent luminance and favorable efficiency of light emission.
Resolving the above problems, for example, U.S. Pat. No. 5,645,948 discloses an organic EL device with the use of a compound having benzimidazole structure as an light emitting material describing that the organic EL device emits light with a luminance of 200 nit at a voltage of 9 V. Further, Japanese Unexamined Patent Application Laid-Open No. 2002-38141 discloses a compound having benzimidazole ring and anthracene skeleton. However, an organic EL device with further enhanced luminance and with further improved efficiency of light emission than the organic EL device with the use of the above compounds is required.